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Pine Beetle Infestation Under the Presidents’ Noses

Hands-off care of the forests around Mount Rushmore may have created a sweet spot for an ancient enemy of the Ponderosa pine — the mountain pine beetle.

Here, on the western flank of Mount Rushmore, from the vista that highlights George Washington's 60-foot profile, a few Ponderosa pines are showing signs of autumnal shedding. Nothing indicates anything amiss right under the immortalized presidents' stony noses. Yet not far from where Crazy Horse and Custer once rode, South Dakota's historic Black Hills are again rife with warfare, that of the dread mountain pine beetle's assault.

Since the 1997 onset of this latest beetle epidemic, several million Ponderosa pine trees have been killed; a third of Black Hills National Forest's  1.2 million acres are impacted.

Forests around the Mount Rushmore National Memorial itself only came under attack earlier this year. Although details are sketchy, memorial officials now acknowledge that the tiny beetle has ravaged at least a dozen trees inside the park's carefully tended setting.

"We don't have a full understanding of the scope of the problem," said Bruce Weisman, director of resource management at the memorial. "We do know that the Black Elk Wilderness to our west has a lot of tree mortality. That puts all the trees in jeopardy. A catastrophic wildfire here would clear out all these trees."

The pine beetle has been a feature of the Black Hills for the last 10,000 years, or at least since the days when an ice age-era glacier essentially bisected South Dakota near what is now the Missouri River. Today, the Black Hills are essentially a forested island surrounded by a sea of grass.

In modern times, the first recorded beetle outbreak hit the Black Hills in the late 1890s, when over 20 years an estimated 10 million trees were killed. Nearly a century later, a 1970s outbreak destroyed more than 440,000 trees.

As for this most recent outbreak?

"Probably about a fifth of the acreage in the Black Hills has or had infested trees," said John Ball, a forest ecologist at South Dakota State University. "In some areas, mortality is nearly 100 percent. This is definitely worse than the 1970s, but still below the greatest outbreak that occurred in the 1890s."

Why has the area been hit with yet another beetle infestation?

Forest management practices, especially the elimination of fire, as well as drought in the previous years, have made the forest very susceptible to intense beetle outbreaks, says research ecologist Amy Symstad at the U.S. Geological Survey's Black Hills station in Hot Springs, S.D.

Beetle trouble really begins in late June or July, when black to rusty brown adult beetles, roughly a quarter-inch long, start burrowing into the lower three-quarters of the tree where they lay eggs and spend the winter.

The eggs become larvae that, in turn, feed on the tree until the larvae pupate and eventually emerge as new adults. The beetle larvae destroy their pine hosts by disrupting the flow of food from the trees' needles to their roots while also spreading the deadly fungus, Ceratocystis montia.

"The pine trees' defense is resin," Ball said. "But the beetle has realized that if you try to attack a pine by yourself, you're going to die because that tree is probably going to be able to produce enough sap to pitch you out. So their best bet is to attack the trees en masse."

To help give high-value, old-growth Ponderosa pines inside the memorial a fighting chance, the National Park Service has already sprayed 740 trees with Sevin, an insecticide that should remain deadly for at least a couple of years.

"We are ahead of this right now and have made significance progress in the last year," Weisman said. "We plan to continue spraying for the next four years and have already identified 1,800 trees for spraying next year. As we learn more about how this is spreading geographically in the memorial, we can proactively plan how to respond. Infested trees will be taken out later this fall."

The ultimate root of the problem may lie in the over-density of the forest itself.

"Trees literally grow like weeds out here," Ball said. "Ponderosa pines don't die, they stagnate."

Forests around Mount Rushmore and across the Black Hills used to have 100 trees per acre. Today, that number can range up to 10,000 trees per acre.

Thus, the National Park Service is implementing a forest thinning project at Mount Rushmore to reduce the density of trees 10 inches in diameter or less in many parts of the park in order to reduce the probability of widespread fire in the memorial. The park service hopes the thinning may also reduce the beetle impact.

"No one is going to eliminate the beetle," Ball said. "It's a natural part of our forest system. But the ultimate solution is to manage the forest by proper thinning. We can thin it or the beetle will thin it for us."